This invention relates generally to combine harvesters and is more specifically concerned with the cleaning mechanisms of such machines.
In a combine harvester, the incoming crop material is threshed and separated in the threshing and separating mechanism and the separated grain falls onto a grain pan, together with a certain amount of foreign material such as chaff and dirt; the grain pan being located beneath the threshing and separating mechanism. The grain pan is reciprocated longitudinally of the machine and is arranged so that this reciprocation moves the material thereon progressively rearwardly whilst at the same time effecting initial separation into layers of the heavier grain kernels and the lighter straw, chaff and other foreign material. These layers are then transferred to an upper or chaffer sieve which is also reciprocated and through which air is blown so as to render airborne the lighter foreign material for discharge from the rear of the machine. The grain falls through the upper sieve to a lower sieve, which also is reciprocated and has air blown through it to remove any remaining foreign material. The clean grain then falls through the lower sieve to a clean grain trough from where it is conveyed to the grain tank. Any straw which remains on the upper sieve is discharged from the rear end thereof for subsequent discharge to the ground.
The terms "grain", "straw" and "tailings" are used principally throughout this specification for convenience and it should be understood that these terms are not intended to be limiting. Thus "grain" refers to that part of the crop material which is threshed and separated from the discardable part of the crop material which is referred to as "straw". Incompletely threshed ears are referred to as "tailings". These terms are used irrespective of the type of crop under consideration. Also terms such as "forward", "rearward", "left", "right", etc. used in connection with the combine harvester and/or components thereof are determined with reference to the direction of forward operative travel of the combine harvester but should not be considered as limiting.
The entire cleaning mechanism, including the grain pan, is highly critical to the loading thereof and operates most efficiently when the grain pan and sieves are loaded evenly, i.e. when they have a uniform layer of material thereon as seen across the transverse width thereof. It will be appreciated that this uniform loading is difficult to achieve in practice, in the absence of special steps, because firstly the layer of crop material fed to the threshing and separating means may of itself already be non-uniform which means that the threshed grain issuing therefrom is also non-uniformly distributed across the width of the cleaning apparatus and secondly, the loading of the cleaning apparatus is very susceptible to the sideways or lateral inclination of the machine. Thus, if a combine harvester is working on the side of a hill, the cleaning mechanism will tend to be heavily loaded at the lower side and lightly loaded, if at all, at the upper side. If the grain pan and sieves are divided into longitudinally-extending sections, then each section is mis-loaded in the same way.
In one known combine harvester illustrated in GB-A No. 2.052.238, the whole cleaning mechanism is pivotable about an axis extending longitudinally of the machine and the lateral inclination of the machine is sensed and the cleaning mechanism driven accordingly about the pivot axis so as to maintain the mechanism substantially horizontal at all time. This is an excellent solution to the problem but it is expensive.
In other combine harvesters such as examplified in FR-A-No. 2.328.391 and GB-A-No. 1.313.802, the sieves are formed by a plurality of interconnected, longitudinally-extending sections, each of which is pivotable about a fore-and-aft axis of the machine, whereby it can be maintained substantially level, as seen in the transverse direction of the machine, irrespective of the lateral inclination of the machine. This has proved to be a valuable expedient in that, dependent upon the degree of lateral machine inclination, the capacity of a machine can be increased by up to 20% but does not provide a full solution to the problem.
In SU-A-No. 1.119.630 there is disclosed a combine harvester in which the grain pan is provided with movable deflectors or dividers which are operable to spread the grain uniformly over the pan. The deflectors are actuatable manually from a common drive mechanism which is not a practicable proposition in that the lateral inclination of a machine changes constantly and an operator cannot afford to stop the machine and adjust the grain pan deflectors each time it is necessary.
Accordingly, there is a need for an improved cleaning mechanism for a combine harvester which is less expensive than the entirely pivotable mechanism referred to above but which nevertheless effects a significant improvement in the cleaning capacity of the machine.